Diesel combustion may generate emissions, including particulate matter (PM). The particulate matter may include diesel soot and aerosols such as ash particulates, metallic abrasion particles, sulfates, and silicates. When released into the atmosphere, PM can take the form of individual particles or chain aggregates, with most in the invisible sub-micrometer range of 100 nanometers. Various technologies have been developed for identifying and filtering out exhaust PMs before the exhaust is released to the atmosphere.
As an example, soot sensors, also known as PM sensors, may be used in vehicles having internal combustion engines. A PM sensor may be located upstream and/or downstream of a diesel particulate filter (DPF), and may be used to sense PM loading on the filter and diagnose operation of the DPF. Typically, the PM sensor may sense a particulate matter or soot load based on a correlation between a measured change in electrical conductivity (or resistivity) between a pair of thin electrodes placed on a planar substrate surface of the sensor with the amount of PM deposited between the measuring electrodes. Specifically, the measured conductivity provides a measure of soot accumulation.
An example PM sensor is shown by Goulette et. al. in US 2015/0153249 A1. Therein, a conductive material disposed on a substrate is patterned to form interdigitated “comb” electrodes of a PM sensor. When a voltage is applied across the electrodes, soot particles are accumulated at or near the surface of the substrate between the electrodes.
The inventors herein have recognized potential issues with such systems. As an example, in such PM sensors, only a small fraction of the PM in the incoming exhaust experiences the electrostatic forces exerted between the electrodes and gets collected across the electrodes formed on the surface of the sensor, thereby leading to low sensitivity of the sensors. Further, even the fraction of the PM that is accumulated on the surface may not be uniform due to a bias in flow distribution across the surface of the sensor. The PM may tend to accumulate mostly, or strictly, at the inlet side of the sensor, and achieve low, and/or non-uniform soot loading. The non-uniform deposition of the PM on the sensor surface may further exacerbate the issue of low sensitivity of the sensor.
The inventors have recognized the above issues and have identified an approach to at least partly address the issues. In one example, the issues above may be addressed by a particulate matter sensor, including: a first conductive matrix having a three dimensional shape defined by non-negligible dimensions in an x-dimension, a y-dimension, and a z-dimension to be charged to a first voltage to function as a positive electrode; and a second conductive matrix having a three dimensional shape defined by non-negligible dimensions in the x-dimension, the y-dimension, and the z-dimension to be charged to a second voltage to function as a negative electrode. One of the first and second matrices may define extensions and/or passages, and the other of the first and second matrices may define extensions and/or passages. The extensions and/or the passages may pass respectively through, and/or near, each other forming multiple soot capturing gaps defined by a local shortest distance from the first matrix to the second matrix. A first of the multiple soot capturing gaps may be oriented orthogonal to a second of the multiple soot capturing gaps. A change in voltage of the first and/or second matrix may be effected by soot forming in the soot capturing bridges and may be determinable as a soot concentration level in an exhaust stream from an engine. In this way, soot capture may be better distributed and more uniform, and the sensitivity and reliability of the sensor may be improved.
As one example, an exhaust PM sensor assembly may be positioned downstream of an exhaust particulate filter in an exhaust passage. The PM sensor assembly may be a box-type sensor and may include sealed bottom, top, and side surfaces, and may further include open front, and rear surfaces, for directing exhaust inside and out of the assembly.
Overall, these characteristics of the sensor assembly may cause an output of the sensor assembly to be more accurate, thereby increasing the accuracy of estimating particulate loading on a particulate filter.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.